Automatic television tracker systems including television point trackers or area correlation trackers operating with compatible sensors such as vidicons have been found capable of meeting the requirement for system pointing accuracies on the order of tenths of a milliradian. The tracker measures any alignment error between the line of sight to the target and the optical system pointing vector and issues error signals which command the system servos to correct the system pointing vector to achieve the desired result.
For a truly effective fire control system, the laser beam to be directed at the distant target must be boresighted to the television and/or FLIR tracker systems. Prior boresighting systems include those which sight the laser designator when separated from the launcher (ground, sea or air based), such as during initial assembly only, or at scheduled intervals in a maintenance shop. Other systems permit boresighting while the laser pod is installed on the launching vehicle. However, these prior art systems are limited to occasional boresighting on laser secure ranges or to flight line boresighting to each mission of an aircraft. The system which would allow for the smallest boresight error over many missions is the type which is based upon airborne boresighting. Airborne boresighting techniques may involve the alignment of the laser optical axis only at the beginning of the mission in response to a pilot initiated command, or boresighting may be initiated each time the fire control system is activated.
Examples of known boresighting techniques are given in U.S. Pat. No. 3,628,868 issued Dec. 21, 1971 to Starkey and U.S. Pat. No. 3,752,587 issued Aug. 14, 1973 to Meyers et al. Starkey shows a laser boresight device which has a telescope mounted on the housing of the laser and accomplishes boresighting through manual micrometer adjustments. Meyers discloses a boresighting device which utilizes a strip of material to which the laser is directed during the boresighting operation. The laser burns a hole through the strip allowing light to pass through to the television sensor. The image thus created is aligned on the television camera through the manual adjustment of the horizontal and vertical potentiometers, which center the image with respect to optical crosshairs. Neither of these references disclose automatic boresighting, and this fact is quite significant when it is realized that a pilot, for example, is preoccupied with aircraft flight tasks, and in such circumstances cannot perform manual laser boresighting accurately and reliably.
U.S. Pat. No. 4,155,096 issued May 15, 1979 to Thomas et al taught automatic laser boresighting. These patentees achieved boresighting the laser of a laser designator system to the null point of an automatic television tracker, by selectively causing the laser beam to be retroreflected to the video sensor of the system, which interfaces with a television tracker. The tracker locks onto the retroreflected laser spot, with the tracker error signals being used in a feedback control loop to control the video sensor raster bias. The raster bias voltages center the video sweeps about the laser spot, thereby nulling the tracker error signals and achieving boresight with the laser automatically.
It is well known that certain missiles are designed to h=launched from a land-based, water-based or flight vehicle, and then guided to a selected target by means of optical guidance, radar guidance or the like. One such system of interest to this invention involves a land-based vehicle having a number of launch tubes for rocket powered missiles, which missiles are guided to their target by means of a beamrider guidance system.
The means for tracking a ground to air missile may, for example, utilize TV as well as FLIR (Forward Looking Infra Red) sensors mounted on the launch vehicle to enable the target, for instance an aircraft, to be tracked in daylight as well as during times of poor visibility. On such a vehicle are not only these components, but also a plurality of zoom optic systems, such that the missile may be accurately tracked by a first optical subsystem, and then concentrated guidance information sent to the missile by a second optical subsystem during the rocket motor burn phase, when the plume from the motor is difficult to penetrate. Then, terminal guidance is provided by a third optical subsystem during the unpowered or coast phase of the missile, when precise guidance commands to the missile are extremely important if the target is to be intercepted.
As explained at length in the Amon and Masson invention cited above, a Zoom Projection Optic (ZPO) device provides an electromagnetic radiation beam guidance system which spatially encodes a guidance beam cross-section to develop a large number of resolution elements Each resolution element is uniquely designated by a digital code effected by frequency modulating the radiation in each resolution element according to a different digital word. In other words, a "guidance corridor" is created, enabling the missile to continuously derive up/down and left/right signals and bring about a correction of the flight path of the missile to the central resolution element of the matrix of elements. The ZPO optical device, through which laser energy is directed, is employed for the terminal guidance of the missile.
The ZPO device is preferably utilized in conjunction with a pair of counter-rotating reticle wheels, that are used to spatially encode the guidance beam cross section to develop a large plurality of resolution elements used in terminally guiding the missile. More details of such reticle wheels are to be found in the U.S. Patent to Allen C. Layton, U.S. Pat. No. 4,299,360, issued Nov. 10, 1981. During boresighting, these reticle wheels are disposed in a preestablished stationary position in order to define a highly accurate line of sight. This optical path is utilized to align the other optical components of the system, to permit proper boresighting.
It was as a result of efforts to achieve boresight on a rapid and highly accurate basis that the present invention was developed.